From: Robert Klemme <shortcutter@...>
Date: 2009-11-11T23:40:40+09:00
Subject: Re: Calling a subprocess with specific arguments and capturing its 	output?

2009/11/11 Dan Q <quinxex@gmail.com>:
> On Tue, Nov 10, 2009 at 9:48 PM, Tony Arcieri <tony@medioh.com> wrote:
>> On Tue, Nov 10, 2009 at 4:00 PM, Dan Q <quinxex@gmail.com> wrote:
>>
>>> I was looking for a function with a syntax that allows
>>> separate arguments, like system("du", "-sh", filename)
>>>
>>
>> Why is this any harder than?
>>
>> `#{cmd} #{args.map { |arg| arg.to_s.inspect }.join(' ')}`
>
> That comes a lot closer to working than I had expected ;)
> I'd rather not deal with escaping, at all. Won't shell commands in
> backticks be run differently, depending on what the system shell is?
> I'm not sure whether all unix shells have similar escaping syntax.
>
> The escaping done by inspect() seems to fail when the filename begins
> with whitespace or contains a newline.

If you are on 1.9, escaping is superfluous: you can pass an Array of
arguments directly:

irb(main):001:0> IO.popen(%w{echo *}, "r") {|io| puts io.read}
*
=> nil
irb(main):002:0> IO.popen(["ls", "-a", "-F"], "r") {|io| puts io.read}
./
../
=> nil

This is a lot safer, significantly less error prone and is probably
more efficient as well (because there is no shell needed for parsing
the command line).

As far as I can see this does not work in 1.8.7.

Kind regards

robert


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